Lung Cancer is the leading cause of death from cancer worldwide. Chemotherapy is the mainstay of treatment for lung cancer. However, less than a third of patients with advanced stages of non-small cell lung cancer (NSCLC) respond to the best two chemotherapy drug combinations. Therefore, novel agents that target cancer specific biological pathways are needed.
The epidermal growth factor receptor (EGFR) is one of the most appealing targets for novel therapies for cancer. EGFR plays a major role in transmitting stimuli that lead to proliferation, growth and survival of various cancer types, including, but not limited to, NSCLC. Ligand binding to the EGFR receptor leads to homo- or heterodimerization of EGFR with other ErbB receptors. EGFR is overexpressed in a large proportion of invasive NSCLC and in premalignant bronchial lesions. Bronchioloalveolar carcinoma (BAC), a subtype of non-small cell lung cancer, represents the major form of lung cancer in non-smoking females and is rising in frequency, and epidermal growth factor receptor (EGFR) is expressed with high frequency in BAC. Unfortunately, the response of BACs to conventional chemotherapy is poor. Activation of EGFR leads to simultaneous activation of several signaling cascades including the MAPK pathway, the protein kinase C (PKC) pathway and the PI(3)K-activated AKT pathway (FIG. 1). EGFR signaling translated in the nucleus leads to cancer cell proliferation and survival.
Targeted therapy against the EGFR receptor has produced response rates of 25-30% as first line treatment and 11-20% in 2nd and 3rd line settings (e.g., chemo-refractory advanced stage NSCLC). For example, in phase II clinical trials, 11-20% of patients with chemo-refractory advanced stage NSCLC responded to treatment with the EGFR tyrosine kinase inhibitor gefitinib (commercially available as Iressa®, ZD1839). A trial evaluating the activity of the EGFR inhibitor, erlotinib (Tarceva®, OSI-774) has been completed and the results will be reported in the near future. A retrospective analysis of 140 patients responding to treatment with gefitinib revealed that the presence of BAC features (p=0.005) and being a never smoker (p=0.007) were the only independent predictors of response to gefitinib. These data suggest that EGFR inhibitor therapy is more active in BAC and in non-smokers.
However, currently, there are no selection criteria for determining which NSCLC patients will benefit from treatment with EGFR inhibitors such as gefitinib. Moreover, EGFR expression does not predict gefitinib sensitivity. Therefore, despite the correlation of tumor histology and smoking history with gefitinib response, it is of great importance to identify molecular molecules that influence gefitinib responsiveness, and to develop adjuvant treatments that enhance the response. To accomplish this goal, there is a need in the art to define critical aspects of EGFR signaling and to identify which molecules interact with the EGFR pathway to dictate responsiveness to EGFR inhibitors.